The invention is based on a method for producing a packaging container having a pressure relief valve as set forth herein. In a known method of this kind, disclosed in German Offenlegungsschrift No. 31 47 321, for instance, the pressure relief valve is first assembled from its individual parts, with a sealant, such as silicone oil, being added at the same time. Next, this valve is placed so as to coincide with a opening through which gas can flow that has been punched out beforehand from a strip of packaging container material, and the peripheral flange of the valve is heat-sealed to the inside of the packaging material. In practice, pressure relief valves of this type are manufactured in great quantities, separately from the packaging containers, and are then gathered and brought to a packaging machine in bundles containing a large number of valves; there, they are separated again and then heat-sealed to a pack aging container, or to a strip of packaging material from which packaging containers are then made. Experience has shown again and again that when pressure relief valves of this kind, equipped with a fluid sealant, are transported, or while the already assembled pressure relief valves are in storage, small quantities or traces of the sealant get into the area of the peripheral flange of the valves and into the area of their heat-sealing faces. As a result, when the valves are heat-sealed to the thermoplastic inner layer of the packaging container, portions of the heat-sealing face of the securing flange that are moistened with sealant fail to undergo proper sealing, because the silicone oil used as a sealant acts like an insulating film to inhibit heat-sealing. Such interruptions in the sealed seam between the valve and the packaging container are not gas-tight, allowing air to enter, and oxygen from the air damages the oxygen-sensitive product contained in the package.
European Pat. No. A 12874 also discloses a method for sealing off a pressure relief valve for a packaging container. In this method, fluid sealant is deposited on the edge of the sealing membrane after the individual parts of the valve have been assembled. By capillary action, the viscous sealant then enters in between the membrane and the carrier element, preventing gas diffusion between these parts.